It appears and IS noted as part of Google and even lists the alert within Google's credible security alerts - HOWEVER, it is a sophisticated phishing scam! Hackers identified a flaw that clears DKIM security measures!
Google is working on a fix though be very wary of any AUTHENTIC Google ALERTS!
More details here:
www.pcmag.com
Google is working on a fix though be very wary of any AUTHENTIC Google ALERTS!
More details here:

Watch Out for This Sophisticated Phishing Email That Looks Like It's From Google
Google says it's rolling out a fix but here's what you should do now to protect yourself.